The present invention relates to a memory unit. More particularly, the present invention relates to control technology of the memory unit that employs a semiconductor memory unit. For example, the present invention relates to technology that is applied to a card type memory unit which is formed in a card shape and capable of attaching to a data processing system such as a PDA (Personal Digital Assistant).
In most cases, a hard disc device has been employed as an outer memory unit for a data processing device such as a computer system. In recent years, the outer memory unit, which utilizes a semiconductor memory unit, having large capacity has been employed instead of this hard disc device. A memory device of this type memory unit is structured by plural flash EEPROMs, for example. The memory unit utilizing flash EEPROM in this way can access data at high speed, compared with a hard disc device, and has superior characteristics in the points of reliability and anti-shocking. Such a memory device, is therefore developed as a memory board, a memory card, or a silicon disc device having the same interface as the hard disc, etc.
According to Japanese Patent Application Laid-Open No. Hei 7(1995)-36759, an IC card is disclosed, which includes a card controller for controlling the inside of a card and a microcomputer for controlling a card controller and file data, uses mask ROM and a flash memory for file data storing memory as a local memory and shares its mask ROM as an attribute storing memory. Further, it is aimed to improve the speed of writing a memory, grow longer the span of life, reduce the price, and improve the reliability by using PSRAM as a control table as a part of data management information (information for uniforming rewriting number of times by recording rewriting number of times), a write buffer for improving writing speed and a garbage buffer at the time of erasing unnecessary data.
Further, in accordance with Japanese Patent Application Laid-Open No. Hei 5(1993)-334506, the body system of the outside, in which an IC memory card 10 is equipped, accesses an attribute memory by controlling a mode control circuit 13. Then, there has been proposed an IC card, which controls an area that is required for performing a program and data by selecting one of memories to which data should be written by way of a higher level application program by identifying information of writing data, a reading out processing method, a memory type by each different memory capacity, and allocating addresses.
In accordance with Japanese Patent Application Laid-Open No. Hei 6(1994)-52674, flash EEPROM of the first mass storage unit is mounted on a printing circuit board, and flash EEPROM of the second mass storage unit is also mounted on the same printing circuit board. In this case, flash EEPROM of the second mass storage unit is mounted detachably by way of an IC socket. Thus, since it is possible to exchange flash EEPROM, in which management information is stored, by each chip unit, it is possible to maintain the mass storage subsystem.